During first year, Barty became close friends with Evan and didn’t really know Ami yet. By the time they got to second year, Barty officially met Ami but didn’t talk to her much. By third year, Evan started to develop a crush on Barty. However, this is when Barty started to fight with his dad more often and did things to rebel. He’d start flirting and smoking from a young age and breaking the rules just for fun. Because Evan wanted to be around him, he started doing the same things to fit in. By fourth year, Ami developed a hallway crush on Barty. She’d rant to Remus about it but he’d always warn her since he knew Barty was a bad influence. By fifth year, Ami and Barty started to talk more often. At the start, Barty didn’t really like her and Ami would act like she hated him to cover up her crush. By sixth year, Ami and Barty got closer and Barty eventually caught feelings for her. The two of them started dating, leaving Evan heartbroken. Ami did realize overtime that Evan did have feelings for Barty and would get jealous anytime they hung out. This led to both Evan and Ami hating each other and doing petty things just to make Barty jealous and get his attention. Sometime in seventh year, Evan gave up because he had to take the dark mark and he thought Barty genuinely loved Ami. But by the end of seventh year, Barty realized that even though he did love Ami, he loved Evan more. Barty decided he was going to get the dark mark for Evan and asked Ami to join him as a friend right after breaking up with her, Ami didn't know this was a different alter at the time. Ami declined his offer and blamed Evan for Barty becoming a death eater and then ended up joining the order right after graduation.
During the war, Evan found a way to switch sides and asked Barty to come with him. However, it turned out it was another persona in control named Mr.January and he declined the offer. Evan left thinking Barty has changed and gone crazy and Barty believed that Evan abandoned him. After the war ended, both Barty and Ami went no contact for about ten years with the exception of Ami talking to Remus, Sirius and Rowan. Meanwhile Evan decided to restart his life and open up a bookshop and make new friends. Eventually, Barty decided that he wanted to kidnap Evan so he could find a way to bring back Voldemort. However, this backfired because he found out he had DID and he still loved Evan. After a few dates and with the help of Remus and Sirius, Evan and Barty finally got into a relationship and we’re happy. Barty still found himself thinking of Ami from time to time though. So he told Evan about this and said he wanted to talk to her. Evan tried telling him it was a bad idea but gave up when he realized that Barty still needed to see her at least one last time. So Barty goes to Remus and after a lot of effort manages to convince him to get Ami’s number. Barty calls Ami and asks to meet up and Ami agrees. Ami thinks that because Barty is suddenly wanting to meet up, she may still have a chance because of all the future plans they made in the past. But at the meet up, Barty reveals that he’s with Evan and tells her about the past ten years. Ami tells him about the past ten years as well but gets a call and eventually has to leave. As soon as Ami is gone, Barty realizes that a small part of him does love her even though he still loves Evan more and this causes him to break down in tears for feeling like a bad partner for liking another person. Evan finds him crying and asks him what’s wrong but Barty refuses to tell him and only apologizes. A few days later, Ami calls Barty wanting to meet up again and Barty decided it would be a good idea to invite all of the old friends from Hogwarts for dinner. So everyone comes over and Ami and Evan see each other again for the first time. At this point, Evan is perfectly fine with Ami but Ami is still a bit petty towards Evan. Ami not being able to handle seeing Barty with Evan, makes an excuse to leave early.